Glaucoma is well known as a condition in which the internal pressure in the eye increases to the extent that it causes damage to the optic nerve and may eventually cause blindness. This condition is primarily caused by the failure of aqueous humor to properly drain from the eye, resulting in a high internal or intraocular pressure. It has been recognized that the formation of aqueous humor is in part the result of the activity of the enzyme carbonic anhydrase which is employed by the human body to reversibly catalyze the hydration of carbon dioxide. Compounds, principally heterocyclic sulfonamides, are known which inhibit the activity of carbonic anhydrase and thus control the production of aqueous humor and the intraocular pressure resulting therefrom. [Havener, Ocular Pharmacology, 4th Ed. (1978, C. V. Moseby); Maren, Investigative Ophthalmology, Vol. 13, pp. 479-484 (1974); Becker, Am. J. of Ophthalmology, Vol. 39, p. 177 (1955)].
It is necessary to administer these materials parenterally in order to achieve intraocular pressure reduction. Parenteral administration requires relatively large dosages and very often results in the patient experiencing fatigue, depression, anorexia, numbness and tingling sensations.
It has now been discovered that certain carbonic anhydrase inhibitors can be administered topically, i.e., applied directly to the cornea, and that these compounds will penetrate the cornea and be immediately effective in inhibiting the activity of carbonic anhydrase and decreasing intraocular pressure and aqueous humor flow resulting from this activity.
The topical or local applicability of intraocular pressure depressants offers several major advantages over drugs requiring parenteral administration. Topical applicability avoids the unpleasant side effects described above which result from systemic applications of carbonic anhydrase inhibitors. In addition, topical application enables a more rapid, localized concentration of the drug at the situs requiring the drug's action.